<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <button id="btn1">按钮1</button>
  <button id="btn2">按钮2</button>
  <button onclick="fn()">按钮3</button>



  <script>
    // 兼容性最好
    const btn1 = document.getElementById('btn1')
    btn1.addEventListener('click',() => {
      alert('点击了按钮一')
    })

    // 简洁
    const btn2 = document.getElementById('btn2')
    btn2.onclick = () => {
      alert('点击了按纽二')
    }

    // react推荐使用下面这种方法绑定事件
    function fn(){
      alert('点击了按钮三')
    }
  </script>
</body>
</html>